Re: [PATCH v2 3/3] drm/xe: Change return type of detect_bar2_dgfx() from s64 to u64

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Thu, Oct 16, 2025 at 10:57:40AM +0100, Matthew Auld wrote:
> On 10/10/2025 00:02, Shuicheng Lin wrote:
> > The function never returns a negative value, and the return value is
> > assigned to a u64 variable. Use u64 for better type correctness
> > and clarity.
> > 
> > v2: add assert to catch theoretical negative or zero stolen size. (Rodrigo)
> > 
> > Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>
> > ---
> >   drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c | 4 +++-
> >   1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c b/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c
> > index 9b00bdc8ef1a..e368b2a36bac 100644
> > --- a/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c
> > +++ b/drivers/gpu/drm/xe/xe_ttm_stolen_mgr.c
> > @@ -81,7 +81,7 @@ static u32 get_wopcm_size(struct xe_device *xe)
> >   	return wopcm_size;
> >   }
> > -static s64 detect_bar2_dgfx(struct xe_device *xe, struct xe_ttm_stolen_mgr *mgr)
> > +static u64 detect_bar2_dgfx(struct xe_device *xe, struct xe_ttm_stolen_mgr *mgr)
> >   {
> >   	struct xe_vram_region *tile_vram = xe_device_get_root_tile(xe)->mem.vram;
> >   	resource_size_t tile_io_start = xe_vram_region_io_start(tile_vram);
> > @@ -105,6 +105,8 @@ static s64 detect_bar2_dgfx(struct xe_device *xe, struct xe_ttm_stolen_mgr *mgr)
> >   		return 0;
> >   	stolen_size = tile_size - mgr->stolen_base;
> > +
> > +	xe_assert(xe, stolen_size > wopcm_size);
> 
> This looks to be triggering:
> https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/6359

And when I suggested it I thought it would be useless!
It already caught a bad bug! :)

It looks like we do need to change some logic now and
handle error conditions in this path and block the
code to move forward with invalid initialization.

> 
> >   	stolen_size -= wopcm_size;
> >   	/* Verify usage fits in the actual resource available */
>